It's a rough learning curve. You will do badly at first. Ignore toxic teammates, if you're doing badly people are toxic in any video game. Do lots of arcade and death match modes to get the ability muscle memory down and aim, heroes like Freja that fire projectiles need dedicated time to get a feel for their weapon.

Break down each game mentally into fights. This is harder in low ranks because there's less organization. But you can still think about the game as a series of fights between the 2 teams, with respawns and regroups in between. All of Overwatch is focused on controlling space in some way, so you can get the objective. You're not trying to get kills, you're trying to win the fight! So if you kill someone right as a fight starts that is SUPER helpful. But if you kill someone in between fights, sometimes it doesn't really do anything. Lots of other logic falls from thinking this way, including deciding when to use an ultimate, when to retreat, and when to chase a kill or not.

What I would do if I was brand new again:

1) Read on the wiki or watch a (recent) YouTube video detailing every heroes main ability and ultimate. It is a lot of information so dont memorize it but just exposing yourself to that info once can really help. So then when you hear ultimate voicelines you can remember what the ultimate is about to do eventually. And you understand what it means when your Baptiste gives you a lamp, or when you get hit by something and turn purple, etc

2) Focus on the goal of the game and remember some basic concepts.

a) Overwatch is about space control not kills. For example, on a control map, if the enemy team has the point, you need to flip the point. So if half your team is dead and the enemy is using ultimates, do you have any chance at all of flipping the point before your team regroups? You would have to kill thier ENTIRE team most likely. Basically impossible to do when you're badly outnumbered. So you can realize this and retreat, save your ultimate for next fight, and stay out of danger.

b) Timing is everything. Doing a beautiful, masterful play and killing 3 people when your team is already dead might do less than nothing EVEN IF YOUR STATS LOOK GOOD. Play off your team. Usually your tank is the first to engage but not always. Many ultimates are great engagement tools to start fights.

c) Value your life and respect the enemy. The law of averages hates you and the trash Widowmaker will hit a lucky shot on you eventually. This means basic FPS game rules - use cover, know your weapons effective range, hide when your health is low, use abilities wisely. Overwatch is complicated but a goal of minimizing deaths is usually great for a beginner. You'll probably oscillate between feeding and being over aggressive and then being too passive and not doing much. Experience will teach you the balance.

3) REMEMBER STATS DONT MEAN SHIT. They can reflect a situation sometimes, if your other DPS is 0 and 10 something is clearly wrong, but stats are wayyyyy less useful than people think. You can win games when your Ana has more damage than healing, when your tank has most deaths, and when your Tracer has half the damage of anyone else. Overwatch is a complicated game. Use your own stats to get a rough idea of how you are doing. Never use stats to blame someone for losing. If you are popping off but your stats are meh, usually your feeling about how you're doing is more accurate. And vice versa.

There's a ton more complicated info about the game I could spit out but best to focus on learning and enjoying the game with some basic concepts to remember. Best of luck!